EP0565403A1 - Silica/acrylation dispersions, method for producing them, their use in stereophotolithography and method for preparing articles made of resin - Google Patents

Abstract

Dispersions of colloidal silica in an acrylic ester of an alkanol or a mixture of acrylic esters of alkanols of general formula (I> CH2 = CH - COO - CHR - CHOH - R1 (I> in which either R and R1, which are identical, represent a hydrogen atom or R and R1, which are different, represent a hydrogen atom or a methyl radical, containing from 50 to 70% by weight of silica in the form of discrete polydisperse particles which are not bonded to each other by siloxane bonds and which have a mean diameter between 10 and 50 nm, process for the preparation of these dispersions, use of these dispersions in stereophotography and process for the preparation of articles made of photosensitive resin.

Description

The present invention relates to silicone-acrylic dispersions, their production process, their application in stereophotolithography and a process for the preparation of resin objects.

Stereophotolithography is nowadays more and more used to manufacture complex parts of small dimensions, from photosensitive resins. The resins currently available on the market for this technique do not yet make it possible to obtain objects meeting all the requirements of the user who wishes to have available, at low cost, reliable objects, of good presentation, having excellent mechanical properties and correct aging.

In order to respond to this request, the applicant has discovered with astonishment that certain dispersions of colloidal silica have excellent application properties in stereophotolithography.

Dispersions of colloidal silica in 2-hydroxyethyl acrylate are already known, but to the knowledge of the applicant, these silica dispersions, on the one hand, are monodispersed, that is to say that the dispersed silica particles have substantially all of the same average diameter, and on the other hand they contain by weight less than 50% of silica. These dispersions are easily obtained by mixing, at room temperature, a monodisperse silica hydrosol, in acid form, containing less than 50% by weight of colloidal silica, including the discrete silica particles, not linked together by siloxane bonds, have an identical average diameter of between 10 and 50 nm, with 2-hydroxyethyl acrylate, then removing the water from this mixture, usually by azeotropic distillation under reduced pressure, until obtaining an organosol of silica practically free of water and containing by weight less than 50% of silica.

dans laquelle soit R et R_1' identiques, représentent un atome d'hydrogène, soit R et R_1' différents, représentent, un atome d'hydrogène ou un radical méthyle, caractérisées par le fait qu'elles contiennent pondéralement de 50 à 70% de silice à l'état de particules discrètes, polydisperses, non liées entre elles par des liaisons siloxane d'un diamètre moyen compris entre 10 et 50 nm.This is why the present invention relates to dispersions of colloidal silica in an alkanol acrylate, or a mixture of alkanol acrylates, of general formula (I).

in which either R and R _{1 ′} identical represent a hydrogen atom, or R and R _{1 ′} different represent a hydrogen atom or a methyl radical, characterized in that they contain by weight from 50 to 70 % silica in the form of discrete, polydisperse particles, not linked to each other by siloxane bonds with an average diameter of between 10 and 50 nm.

By "polydisperses" is meant that the study of the dispersion of the particles indicates the existence of several peaks, therefore corresponding to several mean diameters.

Among these dispersions, the subject of the invention is in particular dispersions characterized by the fact
that 20 to 50% by weight of the silica present is in the form of discrete particles, of an identical average diameter, less than or equal to half the average diameter of at least 50% by weight of the remaining silica particles.

Among these latter dispersions, the subject of the invention is in particular a dispersion of colloidal silica dispersed in 2-hydroxyethyl acrylate containing 50 to 70% by weight of silica in the form of discrete particles not linked together by siloxane bonds, having for 40 to 50% by weight of them an average diameter of approximately 13 nm, and for the complement to 100%, an average diameter of approximately 50 nm.

The alkanol acrylates of general formula (I) are either, and preferably 2-hydroxyethyl acrylate, or a mixture in variable proportions of the monoesters of acrylic acid with propanediol-1,2. These monomers are known and they are marketed stabilized with from 0.1 to 0.01% by weight of a stabilizer such as paramethoxyphenol. This stabilizer is kept in the dispersions of the present invention, when using such commercial products.

The invention particularly relates to the dispersions of colloidal silica described in the examples.

The present application also relates to a process for the preparation of the above dispersions, characterized in that a silica hydrosol, monodisperse, in acid form, containing 30 to 30% by weight, is mixed, with stirring 50% silica in the form of discrete particles not linked to each other by siloxane bonds, with an average diameter of 10 to 50 nm with a calculated amount of an alkanol acrylate or a mixture of acrylate d alkanol of general formula (I) above so as to obtain the desired silica content of between 50 and 70% by weight, then distilling the water present in this dispersion, at a temperature below 55 ° C, under reduced pressure and with stirring, to a residual water content of less than 1% by weight, determined by the Karl Fischer method, to obtain a monodisperse dispersion of colloidal silica in alkanol acrylate, or the mixture of alkano acrylates ls of general formula (I) chosen, containing from 50 to 70% by weight of silica in the form of discrete particles not linked to each other by siloxane bonds, having an average diameter of 10 to 50 nm which are isolated or, if desired, it is mixed, at room temperature, in suitable proportions, with one or more other monodisperse dispersions of colloidal silica of desired particle size and adequate silica content, in an alkanol acrylate, or a mixture of acrylates of alkanols of general formula (I) identical and prepared according to the process described above, so as to obtain the desired polydisperse silicoacrylic dispersion tee.

The present application relates in particular to the above process, characterized in that a monodisperse dispersion of colloidal silica particles of a certain diameter is prepared, which is mixed with at least one monodisperse dispersion of colloidal silica particles with an average diameter less than or equal to half the average diameter of the first silica particles, the last silica particles representing 20 to 50% by weight of the silica present, while the first silica particles represent at least 50% of the remaining silica particles.

Its particular subject is the above process, characterized in that 40 to 50% by weight of the silica particles have an average diameter of approximately 13 nm, and the complement to 100% has an average diameter of approximately 50 nm .

Thus, to obtain a dispersion according to the present invention containing 2-hydroxyethyl acrylate, 62.5% of silica in the form of discrete particles having, for 48% by weight of them, an average diameter of 13 nm and for the complement to 100%, an average diameter of 50 nm, identical quantities of a dispersion of colloidal monodisperse silica in 2-hydroxyethyl acrylate containing 60% are mixed at room temperature. weight of silica in the form of particles with an average diameter of 13 nm and of a dispersion of monodisperse colloidal silica in 2-hydroxyethyl acrylate containing 65% by weight of silica in the form of particles d '' an average diameter of 50 nm.

The present invention also relates to dispersions of colloidal silica obtained by the above methods.

The silica hydrosols, monodisperse, in acid form, are obtained by known methods, in particular by leaching of the corresponding commercial silica hydrosol stabilized by an alkaline agent, such as ammonia or an alkali metal hydroxide on a bed of cation exchange resin in acid form. We can quote for example those marketed under the names of KLEBOSOL ^R by the French Company Hoechst.

The silico-acrylic dispersions according to the present invention can be either diluted in all proportions with an alkanol acrylate of general formula (I), to reduce, if desired, their silica concentration, or concentrated under reduced pressure and with stirring, at a temperature below 55 ° C, to raise, if desired, their silica concentration up to 70% by weight.

The silica content of the silico-acrylic dispersions according to the present invention is determined by calcination of a sample of known weight. As for the particle size, it can be determined by transmission electron microscopy or, indirectly, by nitrogen adsorption after drying of the dispersion according to S. Brunauer et al., J. Amer, Chem. Soc., 60, 309 (1938).

The silico-acrylic dispersions according to the present invention have interesting properties in stereophotolithography.

For their application in stereophotolithography, up to 5% by weight of one or more photosensitive polymerization initiators commonly designated photoinitiators is introduced into the dispersions according to the present invention, such as a derivative of a substituted aromatic ketone such as benzophenone, 1-hydroxy cyclohexylphenyl ketone, 2-methyl-2-morpholino paramethylthiopropiophenone. Various conventional additives can also be introduced for this type of application, such as a polymerization inhibitor such as paramethoxyphenol, hydroquinone, a co-initiator, a dispersant, dyes and / or pigments. Generally, the total weight of the additives introduced is less than 10% by weight of the dispersion. Advantageously, in the dispersions according to the present invention intended for stereophotolithography, the level of one or more radical polymerization inhibitors such as paramethoxyphenol or hydroquinone is supplemented, up to 2% by weight, this avoids parasitic polymerizations , and in particular, those induced by the light scattered by the silica particles during their irradiation using an active laser beam.

It is also possible to replace, partially or totally, the photosensitive polymerization initiator (s) with one or more thermal polymerization initiators such as benzoyl peroxide when using a thermal laser of the C0 ₂ type in SPL.

The photosensitive or thermal initiator (s) used, as well as the various additives, are generally introduced into the dispersions according to the present invention, just before their use in stereophotolithography. However, it is advantageous that one or more radical polymerization inhibitors such as paramethoxyphenol, or hydroquinone are present during their preparation.

In stereophotolithography, the dispersions according to the present invention have interesting properties, and in particular they lead during and after the polymerization induced with a laser beam, to very low volume shrinkages.

dans laquelle dm et dp représentent respectivement la masse volumique du monomère et du monomère polymérisé. Ces masses volumiques sont déterminées par les méthodes classiques.We define volume shrinkage by relation (1):

in which dm and dp represent respectively the density of the monomer and of the polymerized monomer. These densities are determined by conventional methods.

To know and study the shrinkage during the polymerization, a thin layer of a dispersion according to the pre is deposited on a dish suspended with wires on a pan of a precision balance. invention, containing 2% by weight of 2-methyl-2-morpholino paramethylthiopropiophenone. After having noted the mass of the sample, the cup is completely immersed in paraffin oil of density 0.86. The difference in the masses of the sample in air and in paraffin oil makes it possible to know its volume. The sample in the paraffin oil is then irradiated with a UV light beam, it polymerizes slowly. The mass of the sample in the paraffin oil varies as a function of the variation in its volume during the polymerization. At the same time, the same experiment is carried out in the absence of monomer and the values obtained are subtracted from the experimental values found with the sample.

Every minute, the volume shrinkage is calculated using the relation (1), then the graph of the volume shrinkage thus calculated is constructed as a function of the polymerization time. It is thus found that with the dispersions according to the present invention, the shrinkage is zero at the start of polymerization, then it increases regularly as a function of time, up to a limit value identical to the value found directly on the polymer by application of the relation (1).

The dispersions according to the present invention also have a good depth of polymerization. This characteristic is an important factor for obtaining objects in stereophotolithography, because a too low polymerization depth does not allow satisfactory adhesion of the layers. Furthermore, due to their good transparency properties, the dispersions according to the invention diffuse little active light, which results in good spatial resolution.

To determine the depth of polymerization, a sample of the dispersion to be tested containing 1% by weight of IRGATURE ^R 500, which is an equal-weight mixture of benzophenone and, is placed in a tank for UV spectrophotometer, of section 1 cm ² . 1-hydroxy-cyclohexylphenyl ketone, then the sample is punctually irradiated with a laser beam for a determined period (1 minute for a laser with a power of 100 mW). The tank is then emptied, the polymer obtained is washed with acetone, then the height of the peak of the polymer formed at the point of impact of the laser beam is measured. For the various dispersions according to the present invention, the heights of the peaks measured vary from 4 to 7 mm, corresponding to a very good depth of polymerization.

The dispersions according to the present invention also have a satisfactory viscosity for producing objects of complex shape in stereophotolithography without problem.

The following examples illustrate the present invention without, however, limiting it.

EXAMPLE 1

8000 g of a silica hydrosol sold under the name of KLEBOSOL ^R 1344 Na by the French company Hoechst are mixed at ambient temperature, with stirring, having a pH of 9.7 and containing 69.6% by weight of water, 0.4% Na ₂ 0 and 30% silica in the form of monodisperse particles, not linked to each other by siloxane bonds and having an average diameter of 13 nm with 708 g (0.9 I) of a resin cation exchanger with sulfonic groups in acid form and with an exchange capacity of 2 eq / 1. After one hour of stirring, the resin is separated from the reaction medium by filtration. This gives approximately 8000 g of an acid silica hydrosol having a pH = 2, and containing approximately 70% water and 30% silica by weight in the form of monodisperse particles with an average diameter of 13 nm.

4130.2 g of the acid silica hydrosol prepared above are mixed, with stirring, at ambient temperature, with 851.3 g of commercial 2-hydroxyethyl acrylate and 17.2 g of hydroquinone. Then, the water present in the reaction medium is distilled with stirring, at a temperature below 55 ° C, under a pressure gradually reduced from 60 to 20 mbar. 2110 g of a silica organosol are thus obtained containing by weight 38.4% of 2-hydroxyethyl acrylate, 0.6% of water determined by the Karl Fischer method, 0.8% of hydroquinone and 60.2% silica in the form of discrete, monodisperse particles, with an average diameter of 13 nm, not linked to each other by siloxane bonds and having at 20 ° C, a density of 1.576 and a Brookfield viscosity of 2200 mPa.s at 780 rpm.

EXAMPLE 2

As before, a hydrosol acid silica is prepared, having a pH = 2.1 and containing by weight 50% water and 50% silica in the form of discrete, monodisperse particles, with an average diameter of 50 nm, not linked together by siloxane bonds, from a stabilized commercial silica hydrosol, having a pH of 9.3 and containing 50% by weight of water, 0.3% of Na ₂ 0 and 49.7% of silica in the form of monodisperse particles, with an average diameter of 50 nm, not linked to each other by siloxane bonds.

Then mixed with stirring and at room temperature, 2808.3 g of this silica acid hydrosol with 611.4 g of 2-hydroxyethyl acrylate and 16.6 g of hydroquinone. Then the water present in the reaction medium is removed by distillation, with stirring, at a temperature below 55 ° C, under a pressure gradually reduced from 60 to 20 mbar. 2035 g of a silicone-acrylic dispersion are thus obtained containing 30.3% by weight of acrylate of 2-hydroxyethyl, 0.8% of hydroquinone, 0.7% of water and 68.2% of silica in the form of discrete, monodisperse particles, with an average diameter of 50 nm, unbound between them by siloxane bonds, and having a Brookfield viscosity, determined at 20 ° C., at 780 rpm of 8000 mPa.s.

This silico-acrylic dispersion is then diluted with 100 g of 2-hydroxyethyl acrylate to bring its silica titer to 65% by weight. A silicone-acrylic dispersion is thus obtained having, at 20 ° C., a density of 1.635 and a Brookfield viscosity of 740 mPa.s, at 780 rpm and containing by weight 33.5% of hydroxy acrylate. 2 ethyl, 0.7% water, 0.8% hydroquinone and 65% silica in the form of monodisperse particles with an average diameter of 50 nm, not linked to each other by siloxane bonds.

EXAMPLE 3

500 g of the silica-acrylic dispersion obtained in Example 1 and 500 g of the silico-acrylic dispersion obtained in Example 2 are mixed with stirring at room temperature. 1000 g of a silico dispersion are thus obtained -acrylic containing 36% by weight of 2-hydroxyethyl acrylate, 0.7% of water, 0.7% of hydroquinone and 62.5% of silica in the form of discrete, polydisperse, unbound particles between them by siloxane bonds, 48% of which by weight, have an average diameter of 13 nm and 52% an average diameter of 50 nm. This dispersion has a density of 1.605.

EXAMPLE 4

666.7 g of the silica acid hydrosol prepared in Example 1 are mixed with room temperature, with stirring, with 200 g of a mixture of acrylic acid monoester with 1,2-propanediol containing 75 % of 2-hydroxypropyl acrylate, 25% of 2-hydroxyethyl methyl-1 ethyl acrylate and 33.4 g of hydroquinone. Then, the water present in this reaction medium is distilled, with stirring, at a temperature below 55 ° C, under a pressure gradually reduced from 60 to 20 mbar. 400 g of a silico-acrylic dispersion are thus obtained, containing by weight 48% of monoesters of acrylic acid with propanediol-1,2, 0.8% of hydroquinone, 0.8% of water and 50% of silica in the state of monodisperse particles, with an average diameter of 13 nm, not linked to each other by siloxane bonds and having at 20 ° C, a density of 1.446 and a Brookfield viscosity, at 780 rpm, of 1528 mPa.s.

EXAMPLE 5

In the dispersion prepared in Example 3, 1% by weight of benzophenone and 1% by weight of 1-hydroxycyclohexylphenylketone are introduced at ambient temperature, with stirring, then with this mixture, preparation is carried out on a stereophotolithography machine equipped with an ionized argon laser source operating in the ultraviolet (351 and 363 nm) a honeycomb cube with 30 mm edge containing 36 parallelepepedic cells, with a mesh grid of 5 mm, with a speed of movement laser beam of 2.4 cm / s, a power of 400 mW and a layer thickness of 0.25 mm. Before the post-polymerization, there is thus obtained a transparent object, of excellent presentation, with thick, regular and well defined walls. After a 90-minute post-polymerization in an oven at 150 ° C, the honeycomb cube is completely hard and has no cracks or traces of silica on the surface. The volume shrinkage is 4% (dp = 1.666).

EXAMPLES 6 AND 7

A honeycomb cube is prepared, as in Example 5, with the dispersions prepared in Examples 1 and 2 into which 1% by weight of benzophenone and 1% by weight of 1-hydroxycyclohexylphenylketone have been introduced. This gives two honeycomb cubes of correct presentation, with transparent and well-defined walls. The volume shrinkage is 6% for the dispersion of Example 1 and 1.5% for the dispersion of Example 2.

COMPARISON EXAMPLE 1

In a commercial dispersion of silica in 2-hydroxyethyl acrylate containing by weight 69.2% of 2-hydroxyethyl acrylate, 0.8% of water and 30% of silica in the form of particles discrete, monodisperse, with an average diameter of 13 nm, having a density of 1.259, a honeycomb cube is prepared as in Example 5 after introduction into the dispersion of 1% by weight of benzophenone and 1% by weight of 1-hydroxy cyclohexylphenyl ketone.

This gives a cube of very poor presentation with puffy walls and poor adhesion between the layers. The volume shrinkage of this dispersion is 15%.

Claims (10)

1. Dispersions of colloidal silica in an alkanol acrylate or a mixture of alkanol acrylates of general formula (I)

in which either R and R _{1 ′ are} identical, represent a hydrogen atom, or R and R _i , which are different, represent a hydrogen atom or a methyl radical, characterized in that they contain 50 to 70% by weight of silica in the form of discrete, polydisperse particles, not linked together by siloxane bonds with an average diameter of between 10 and 50 nm. 2. Dispersions according to claim 1, characterized in that 20 to 50% by weight of the silica present is in the form of discrete particles with an identical average diameter, less than or equal to half the average diameter of at least 50 % by weight of the remaining silica particles. 3. Dispersions according to claim 2, characterized in that they contain, by weight in 2-hydroxyethyl acrylate, from 50 to 70% of silica in the form of discrete particles not linked together by siloxane bonds, having for 40 to 50% by weight of them, an average diameter of about 13 nm, and for the complement to 100%, an average diameter of about 50 nm. 4. Process for the preparation of the dispersions according to any one of claims 1 to 3, characterized in that a silica hydrosol, monodisperse, in acid form, containing 30 by weight, is mixed, with stirring. with 50% silica in the form of discrete particles not linked to each other by siloxane bonds, with an average diameter of 10 to 50 nm with a calculated amount of an alkanol acrylate, or of a mixture of alkanol acrylates of general formula (I)

in which either R and R _{1 ′ are} identical, represent a hydrogen atom, or R and R _{1 ′} different, represent a hydrogen atom or a methyl radical, so as to obtain the desired silica content of between 50 and 70 % by weight, then the water present in this dispersion is distilled, with stirring, at a temperature below 55 ° C, and under reduced pressure, to a residual water content of less than 1% by weight , determined by the Karl Fischer method, to obtain a monodisperse dispersion of colloidal silica in the alkanol acrylate or the mixture of alkanol acrylates of general formula (I) chosen, containing from 50 to 70% by weight of silica in the form of discrete particles not linked to each other by siloxane bonds, having an average diameter of 10 to 50 nm which are mixed, at room temperature, in suitable proportions, with one or more other monodisperse dispersions of colloidal silica e of desired particle size and adequate silica content, in an alkanol acrylate or a mixture of alkanol acrylates of identical general formula (I) and prepared according to the process described above, so as to obtain the silico dispersion - desired polydisperse acrylic. 5. Method according to claim 4, characterized in that a monodisperse dispersion of colloidal silica particles of a certain diameter is prepared which is mixed with at least one monodisperse dispersion of colloidal silica particles of a diameter mean less than or equal to half the average diameter of the first silica particles, the last silica particles representing 20 to 50% by weight of the silica present, while the first silica particles represent at least 50% of the remaining silica particles . 6. Method according to claim 4 or 5, characterized in that 40 to 50% by weight of the silica particles have an average diameter of about 13 nm, and the complement to 100% has an average diameter of about 50 nm . 7. Use in stereophotolithography, as resin, dispersions of colloidal silica in an alkanol acrylate and a mixture of alkanol acrylates of general formula (I)

in which either R and R _{1 '} identical, represent a hydrogen atom, or R and R _i , different, represent a hydrogen atom or a methyl radical, characterized in that they contain 50% to 70% by weight of silica in the form of discrete particles, not linked to one another by siloxane bonds with an average diameter of between 10 and 50 nm. 8. Use in stereophotolithography, as a resin, the dispersions according to any one of claims 1 to 3. 9. Use in stereophotolithography, as a resin, the dispersions according to any one of claims 1 to 3, obtained by the process of any one of claims 4 to 6. 10. A process for preparing photosensitive resin objects, characterized in that a colloidal silica dispersion according to one of claims 1 to 3 or obtained according to the process of any of the claims is used in the conventional process 4 to 6.